Add OFB mode.

Change-Id: I267cf7897b5a9f73f8de729971cb9e92937011dd
diff --git a/include/openssl/cipher.h b/include/openssl/cipher.h
index 1df4699..bc69378 100644
--- a/include/openssl/cipher.h
+++ b/include/openssl/cipher.h
@@ -80,10 +80,12 @@
 OPENSSL_EXPORT const EVP_CIPHER *EVP_aes_128_ecb(void);
 OPENSSL_EXPORT const EVP_CIPHER *EVP_aes_128_cbc(void);
 OPENSSL_EXPORT const EVP_CIPHER *EVP_aes_128_ctr(void);
+OPENSSL_EXPORT const EVP_CIPHER *EVP_aes_128_ofb(void);
 
 OPENSSL_EXPORT const EVP_CIPHER *EVP_aes_256_ecb(void);
 OPENSSL_EXPORT const EVP_CIPHER *EVP_aes_256_cbc(void);
 OPENSSL_EXPORT const EVP_CIPHER *EVP_aes_256_ctr(void);
+OPENSSL_EXPORT const EVP_CIPHER *EVP_aes_256_ofb(void);
 
 /* Deprecated AES-GCM implementations that set |EVP_CIPH_FLAG_CUSTOM_CIPHER|.
  * Use |EVP_aead_aes_128_gcm| and |EVP_aead_aes_256_gcm| instead. */